If you use a spell to throw an object, you don't get any additional stress to your attack - unless you specifically tag/invoke an aspect to get a +2 to attack; you use the normal weapon rating and accuracy of your spell regardless of the object. That is explained easily enough; unless the object in question is in a specifically advantageous position for that attack (i.e. the tag or invoke of an aspect) then all the kinetic energy of the blow comes only from your spell and is exactly the same in both cases. A spell used to throw a car could crush someone with that blow. The same spell used to hurl a knife will impart the same energy to the knife and where the car slammed into the target at a few MPH, the knife will hit at a few miles per second... hitting like an antitank kinetic projectile.
The result? No matter what object you throw, the weapon rating will be the same for the same spell. The advantage of throwing objects instead of blasting directly with magic is not extra damage - it is your attack ignoring magical defenses. The target is behind a threshold? That won't mean much for that knife thrown at him at 5 miles/second. Neither will a magic circle that blocks magic or the target having outright magical immunity.
When you create special effects instead, you use your shifts of power towards that effect instead of weapon rating. Your control is no longer your attack roll because you are not attacking with the spell as a weapon. You create an effect and that effect then becomes the attack (it usually doesn't have a weapon rating)
Ditto for creating a real effect with magic as a maneuver. You don't get any bonuses in the size of the effect - you just get to treat the effect as nonmagical. If you use water magic to turn the ground into mud, it remains mud even after the spell ends (as Harry learned when the Summer Lady tried to drown him in the mud - which remained mud after the Lady left Faerie and drowned him even within a magic circle). If you use earth magic to raise a wall of stone, it remains a wall of stone. If you use fire magic to superheat some rock so it bursts from the ground in a wall of magma, it remains magma even if your spell is instantaneous (as Harry did in a certain cave) and so would turning water into ice by draining heat instead.
Last but not least, there are some more complicated spells - thaumaturgies and thaumaturgies as evocations with sequenced effects. Depending on how you build them, their effects and how they are resolved can vary wildly. For example, a thaumaturgy-as-evocation spirit spell that throws an invisible dart. Assume you got 8 power and 8 control. The spell's power is 7 shifts for a temporary veil on the dart plus 1 shift for weapon 1 on the throw itself. When you cast this spell the following happens;
1) Roll control. That is for controlling the total power and will also be your attack roll.
2) The defender rolls Awareness against the 7-shift veil to notice the dart.
3) If they noticed the dart, they roll dodge normally. If they did not, they roll a 0 for their dodge!
4) They are hit by a weapon 1, attack +8 dart. Calculate stress according to the defense they rolled.
This fairly complex spell is something someone like Molly might use and it is no less lethal for being a mostly-illusion spirit effect. It is quite effective if you expect your enemy to be a fast, agile guy (like a vampire) and also extremely effective if you want to assassinate people in broad daylight without anyone noticing it was you who killed them.